Monthly event showing as daily in Calendar

A monthly recurring event typically shows up as daily in your calendar app because the recurrence rule was accidentally set to repeat every day instead of every month, or an "All-Day" multi-day span was configured incorrectly.

Try this

• Check the Recurrence Rule: Open the event, tap Edit, and look at the repeat frequency. Change it from "Daily" or "Every day" to "Monthly" (or "Every month").
• Verify Start and End Dates: Ensure the start date and end date fall on the same day of the month (e.g., repeating on the 15th of every month) rather than spanning consecutive days.
• Save the Series: When prompted, select All events so the correction applies to the entire repeating series rather than just a single instance. 

If a monthly event is suddenly appearing every day, I'd first check the event's actual Repeat setting rather than assuming it's just a Calendar display issue.

Open one of the events and tap Edit, then look at Repeat. If it says Daily, change it back to Monthly. If you need something specific such as "the first Tuesday of every month," use Custom > Monthly and choose the appropriate day/week.

If it already says Monthly but the event is still appearing every day, I'd try deleting that recurring event and creating it again rather than editing the existing series. There have been reports of recurring Calendar events behaving incorrectly after an iOS update.

Also check the same calendar on iCloud.com. If it shows correctly there but incorrectly on the iPhone, that points more toward a syncing/display issue. If it's wrong on iCloud.com too, the recurrence itself may have been changed.

If you can say which iPhone/iOS version you're using and whether the Repeat setting actually says Daily or Monthly when you edit it, that would narrow this down quite a bit.